1. Field of the Invention
The present invention relates to apparatus and associated methods for inspecting containers to determine the fill line volume of the container.
2. Description of the Prior Art
It has been known in connection with numerous containers to inspect the same for conformance to a wide variety of specifications including, for example, overall dimensions, wall thickness, symmetry, and container capacity. Such containers include rigid containers which may be made of glass, plastic, metal or combinations thereof, for example.
U.S. Pat. No. 4,899,573, owned by assignee of the present invention, discloses a system for inspecting containers for leak and volume by providing a test container and a standard container with pump means delivering to each container a pressure pulse through conduits which contain acoustical impedance means. The pressure differential between the two conduits measured between the standard container and the acoustical impedance in its portion of the conduit and the test container and its portion of the acoustical impedance material is then employed to determine volume differential between the container being tested and the standard container. The disclosure of this prior patent is incorporated herein by reference.
One of the important parameters measured in respect of such containers, particularly rigid containers, which are adapted to hold liquids or other flowable materials is fill point capacity in order to make sure that the containers will deliver the desired amount of the product and to provide a uniform appearance for a group of containers on the store shelf. Also, if the headspace is too small, high pressure can build up in the headspace as the product warms. This can result in container breakage.
One known prior art method for effecting this measurement is to achieve it gravimetrically. The empty container is weighed. The container is then filled to the specified point with water and the container is weighed again. Among the disadvantages of this approach are errors that can be made in measurement, variations in the water fill temperature, and errors in filling to the desired fill point, which errors may be equipment errors if semi-automatic or automatic fill point instruments are employed, or human, if an operator is required to judge the fill point. Also, errors can be made in making the required calculation. As a result, variations can occur with such a test resulting in departure from the desired fill point.
The fill point can be measured as (a) a specific distance from the base of the container, or (b) a specific distance down from the mouth of the container, or (c) on the basis of headspace.
In spite of the foregoing prior art, there remains a need for an efficient, reliable system for determining the volume of a container which will be occupied by a product if the product is provided to a level of a predetermined fill line.